OBJECTIVE: Procedures for the computer simulation of transport processes--especially of velocity sedimentation--have developed to the point of predicting realistically the behavior to be expected of a wide variety of chemically reacting systems of macromolecules. Up to now, the simulation techniques have been used almost entirely to obtain purely qualitative information about associating solutes--to recognize the occurrence of chemical reactions and to place broad limits around the possible nature of the reactions. The first objective of this research is to develop the simulation approach to the point where it can usefully complement other techniques in producing quantitative descriptions of associating systems in terms of reaction stoichiometries and equilibrium constants. The second and more significant objective of the proposed research is to use the simulation technique as a major part of an experimental effort to describe in detail a suspected but presently undefined associating system. APPROACH: Computer simulation has been heavily and fruitfully used to predict qualitatively the behavior of chemically interacting macromolecules during transport experiments. Numerical modelling of the velocity sedimentation of self-associating solutes in the ultracentrifuge is being used to define the chemical equilibria quantitatively in terms of reaction stoichiometry and equilibrium constants. Simulated experiments are being used to consider how nearly unique the boundary shape is for a particular self-associating system. Simulations are being done for various model reactions, and all of the system parameters are being adjusted within physically plausible ranges to make the calculated boundaries given by different models resemble each other as closely as possible. Model calculations are being done to fit experimental sedimentation velocity profiles for various proteins known or suspected to be involved in self-association equilibria.